Thermosetting cement comprising a



United States Patent THERMOSETTING CEMENT COMPRISING A PITCH, A FURFURYLCOMPOUND, CAR- EQgIACEOUS PARTICLES AND ACID CATA- Lester L. Winter andTheodore Edstrom, Lewiston, N.Y., assignors to Union CarbideCorporation, a corporation of New York No Drawing. Application October11, 1955 Serial No. 539,947

3 Claims. (Cl. 260-285) This application relates to a thermosettingcement of a type particularly useful in joining carbon and graphitearticles such as bricks, electrodes, rods, and pipes.

Conventional cements for joining carbon and graphite articles consistprincipally of pitch and a volatile plasticizer. These cements areapplied to the articles to be joined and heated moderately to drive offthe plasticizer and set the cement. These cements have the disadvantageof softening when heated substantially above the melting point of thepitch and losing their strength. Also because they do not set until thevolatile plasticizer is driven off, these cements are ditficult to applyto vertical and uneven surfaces.

The principal object of the present invention is to provide a cement forcarbon and graphite articles which retains its strength at relativelyhigh temperatures.

A further object is to provide a cement suitable for joining carbon andgraphite articles that has a high apparent density upon setting.

Still another object is to provide a cement which has thixotropicproperties such that it remains in position during the time required toharden it.

These objects are accomplished by mixing together, in the properproportions as set forth below, a pitch, a plasticizer, and a catalyst,the pitch having a high melting point, the plasticizer being an organiccompound containing a furfuryl radical, and the catalyst being an acid.These materials, when mixed and blended, form a cement which when heateddoes not soften and retains its strength. The cement of the inventionstifiens readily upon application.

' The pitch used in the cement of the invention should be relativelyfree of volatile constituents so as to minimize the escape of volatilematerials when the cement is heated. The properties required in a pitchto give satisfactory results are as follows: The melting point should bebetween 150 C. and 225 C.; the coking value at 1000 C. should be betweenand the solubility in quinoline should be between 75% and the specificgravity should be not less than 1.25, and the pitch should be compatiblewith furfuryl com pounds at temperatures below C. A melting point ofabout 175 C. is preferred. In general cements containing pitches havingmelting points in the upper part of the range will remain plastic foronly a relatively short period of time, at temperatures of between about60 C. and 75 C. the temperatures at which such cements are mostadvantageously applied. Because of this, cements made with the highermelting point pitches should not be held at application temperatures forprolonged periods of time.

The plasticizer in the cement of the invention is an organic compoundcontaining the furfuryl radical. Examples of suitable compounds arefurfural and furfuryl alcohol. Mixtures of these two materials and amixture of furfuryl alcohol, phenol, and formaldehyde have givenexcellent results. The plasticizer dissolves the pitch at least in partand renders the cement fluid for a time after the constituents aremixed. By increasing or decreasing the ratio of plasticizer to pitch theviscosity of the cement can be decreased or increased, respectively.Upon standing the the presence of the catalyst, the furfuryl compoundspolymerize and thus cause the cement to harden. The polymerization isaccelerated by heating the cement. The rate of polymerization for agiven mixture of pitch and plasticizer can be increased by increasingthe amount of catalyst and heat applied to the cement. This control overthe rate of polymerization permits the formulation of quick setting orslow setting cements to meet specific requirements.

' Best results are obtained when the pitch and plasticizer are presentin the cement in the following proportions: 47% to 55% pitch, 53% to 45%plasticizer. Satisfactory cements have been made with pitch toplasticizer ratios of as high as 6 to 4. The ratio of plasticizer topitch should not be greatly in excess of l to l.

Acids generally have been found to be efficacious as catalysts for thepolymerization of the plasticizer. In the same categoryare acidengendering materials. In the appended claims the term acid catalyst"will be used to designate both acids and acid engendering materials.Particularly good results have been obtained with benzene sulfonylchloride and mixtures of this material with concentrated hydrochloricacid. Other acid catalysts are hydrochloric acid alone, sulfur chloride,sulfuric acid, and boron trifluoride complexes. For most purposes 2%5%catalyst by weight of the cement has been found to be adequate. Noparticular benefits are obtained with amounts of catalyst in excess of10%.

In addition to the materials already specified as essential componentsof the cement of the invention, certain other constituents have beenfound to impart desirable properties to the cement. For cementing roughsurfaces the strength of the cement is improved by the addition to it ofsolid carbonaceous particles. The solid carbonaceous particles should bemilled or otherwise comminuted so that the average particle size is notin excess-of 100 mesh and preferably no larger than to 200 mesh. Thecarbonaceous particles, .for example coke flourand blacks, exert astrong influence on the viscosity of the cement. In addition, acetyleneblack when added to the cement causes the cement to assume an initialset in an exceedingly short time. This property can be employed to holdthe cement in place until the plasticizer is polymerized thusfacilitating its use in places from which a fluid would normally flow.It is preferred to use no more than from 35% to 45% of the particlesbecause with larger amounts the viscosity of the cement is too great.

When solid carbonaceous particles are added to the cement of theinvention, best results have been obtained with compositions within thefollowing range: 20% to 32% pitch, 20% to 32% plasticizer, 30% to 47%carbonaceous particles, and 2% to 10% catalyst.

When heated the cement does not soften as do the conventional pitch basecements of the prior art. Instead enema-91 the cement will coke whenheated sufliciently. In most instances an increase in strength isexhibited by joints prepared with the cement of the invention when thejoint is heated to temperatures above 500 C.

Preferred compositions for cements having a wide range of viscosities atroom temperatures are given in Table I.

Joints are made with the cement of the invention in the conventionalmanner. After the cement is spread on the surfaces to be joined thesurfaces are pressed together and the cement hardened by standing orheating. Best results have been obtained with cements having anintermediate viscosity by applying them to warm surfaces suitably at atemperature .of from about 50 C. to 60 C. The low viscosity cements canbe applied satisfactorily to cold surfaces while the higher viscositycements should be vapplied to surfaces having a temperature of from 20C. to 40 C. Joint strengths in the neighborhood of 1000 pounds persquare inch are common with the cement of the invention.

The advantages to be obtained by using the cement of the invention inmaking joints between carbonaceous arti- .cles .can be seen readily fromthe data in Table II. The data was compiled by making mixtures of thefurfuryl compounds and a number of pitches. The .effect of theproperties of the pitch was determined from the tests.

Of the cements tested and reported in Table II, only those containingpitches numbered 3, 4 and 5 satisfied the requirements of the cement ofthe invention. From the data it can be seen that the cements containinglow a 4 melting point pitches, i.e. melting points of 25 C. and 100 0.,had no appreciable tensile strength when the joints made with them werebaked to temperatures as low as 500 C. On the other hand, the cements ofthe invention had tensile strengths up to 1000 pounds per square inch,and in the case of the cement made with pitch No. 4, actually exhibitedan increase in strength when heated to temperatures as high as 1000 C.

This application is in part a continuation of our application Serial No.323,159, filed November 28, 1952.

What is claimed is:

1. A thermosetting cement capable of retaining its bonding strengthduring and after heating to temperatures as high as 1000 C., comprising20% to 32% of a pitch, 20% to 32% of at least one plasticizer selectedfrom the group consisting of furfural and furfuryl alcohol, 30% to 47%comminuted carbonaceous particles, and 2% to 10% of an acid catalystselected from the group consisting of hydrochloric acid, sulfurchloride, benzene sulfonyl chloride, sulfuric acid and borontrifluoride; said pitch having a melting point of between 150 C. and 225C., a coking value at 1000 C. of from to having a solubility inquinoline of 75% to having a specific gravity of at least 1.25, andbeing compatible with furfuryl compounds at temperatures below C.

2. A thermosetting cement capable of retaining its bonding strengthduring and after heating to temperatures as high as 1000 (1., comprising20% to 32% of a coal tar pitch, 20% to 32% in the aggregate of at leastone of the materials in the group consisting of furfural and furfurylalcohol, 2% to 10% of an acid catalyst, and 30% to 47% of coke flour,said pitch having a melting point of between C. and 225 C., a cokingvalue at References Cited in the file of this patent UNITED STATESPATENTS 2,314,181 Winterkorn Mar. 16, 1943 f 2,383,790 Harvey Aug. 28,1945 FOREIGN PATENTS 639,900 Great Britain July 5, 1950 OTHER REFERENCESAsphalts and Allied Substances" by Abraham, 4th edi tion, pages 478 and479.

1. A THERMOSETTING CEMENT CAPABLE OF RETAINING ITS BONDING STRENGTHDURING AND AFTER HEATING TO TEMPERATURES AS HIGH AS 1000* C., COMPRISING20% TO 32% OF A PITCH, 20% TO 32% OF AT LEAST ONE PLASTICIZER SELECTEDFROM THE GROUP CONSISTING OF FURFURAL AND FURFURYL ALCOHOL, 30% TO 47%COMMINUTED CARBONACEOUS PARTICLES AND 2% TO 10% OF AN ACID CATALYSTSELECTED FROM THE GROUP CONSISTING OF HYDROCHLORIC ACID, SULPHURCHLORIDE, BENZENE SULFONYL CHLORIDE, SULFURIC ACID AND BORONTRIFLUORIDE; SAID PITCH HAVING A MELTING POINT OF BETWEEN 150* C. AND225* C., A COKING VALUE AT 1000* OF FROM 60% TO 80% HAVING A SOLUBILITYIN QUINOLINE OF 75% TO 80% HAVING A SPECIFIC GRAVITY OF AT LEAST 1.25,AND BEING COMPATIBLE WITH FURFURYL COMPOUNDS AT TEMPERATURES BELOW 100*C.